This invention relates to a method for producing a press-in contact having a connection portion to be connected to an electric cable or a circuit of a board, a press-fitting portion to be press-fitted in a through-hole of a printed circuit board, and a contact portion to contact a contact of a mating connector. More particularly, the invention relates to a method for producing a press-in contact which is able to minimize any damage of the contact and a through-hole plated portion, to improve the mechanical property of the contact at its press-fitting portion and in the proximity thereof in order to prevent these portions from being bent or broken, and to stabilize the holding force for retaining the contact in the through-hole owing to the symmetrical shape of the press-fitting portion having no irregularity in shape and size without any rotation of the contact in the through-hole when being press-fitted thereinto.
In general, press-in contacts of this kind are made of a springy copper alloy such as phosphor bronze and beryllium copper. It is ideal to make a press-in contact whose press-fitting portion can apply stresses uniformly to the inner surface of a cylindrical through-hole of a printed circuit board when the press-fitting portion is being press-fitted into the through-hole. For this purpose, with the press-in contact having a press-fitting portion adapted to be forced to reduce its outer diameter enabling it to be inserted into the through-hole, the press-fitting portion has been formed by repeatedly drawing a plate material to obtain finally a U-shaped or V-shaped cross-section whose outer periphery has two arc portions and a straight portion therebetween and whose inner periphery has an inscribing circle whose center is eccentric to the two arc portions.
Moreover, the thickness of the two arc portions in cross-section progressively decreases on proceeding toward the open ends of the U-shaped or V-shaped groove so that the circumferential lengths of the two arc portions contacting the through-hole become longer as much as possible.
With such a known press-in contact, residual stresses are accumulated in the press-fitting portion when being formed so that the mechanical properties in the portion and its proximity deteriorate to decrease its durability, causing the portion to be readily bent or broken by bending stresses. With the known press-in contact, moreover, as the press-fitting portion is formed by repeatedly drawing a plate material so as to be progressively bent to obtain a U-shaped or V-shaped groove, there are in side walls of the U-shaped or V-shaped groove irregularities in shape and size including thickness and length due to slight difference in working for example, by the fact that different parts are worked at different times.
As a result, the outer ends of the side walls of the U-shaped or V-shaped groove frequently do not closely contact the inner surface of the through-hole and the press-in contact tends to rotate in the through-hole so that the contact between the press-fitting portion and the through-hole would become unstable and the holding force therebetween would be decreased.
It is an object of the invention to provide an improved press-in contact which eliminates all the disadvantages of the press-in contacts of the prior art described above and which is durable in use and able to provide stable holding force and stable contact between the press-in contact and a through-hole of a printed circuit board.
In order to accomplish this object, in a method for producing a press-in contact having a press-fitting portion to be press-fitted in a cylindrical through-hole of a printed circuit board, and a contact portion to contact a contact of a mating connector, said press-fitting portion having in cross-section an inner periphery forming a U-shaped or V-shaped groove and an outer periphery including two arc portions and a straight portion therebetween, said inner periphery having an inscribing circle whose center is eccentric to the center of the two arc portions of the outer periphery, and the thickness of said two arc portions in cross-section progressively decreasing on proceeding toward the open ends of walls of said U-shaped or V-shaped groove so that circumferential lengths of said two arc portions contacting the through-hole of the printed circuit board become longer as much as possible, according to the invention said method comprises steps of forming a concaved portion in a block element having a rectangular cross-section at its center by forging, removing both ends of said block element by punching, and then forming the outer periphery of the remaining U-shaped or V-shaped press-fitting portion in cross-section by press-working into arcs which become concentric to said through-hole when said press-fitting portion has been press-fitted and fixed therein.
The press-in contact having the press-fitting portion formed by forging, punching and press-working according to the invention has an advantage of less deterioration of mechanical properties or attributes owing to less working ratio, in comparison with those of the prior art. In other words, the press-fitting portions of the press-in contacts of the prior art have been formed by drawing and bending to generate a great quantity of residual strains in the portions which would act to elongate the portions in lengthwise directions. In contrast herewith, the press-fitting portion of the press-in contact according to the invention is formed by forging, punching and press-working to considerably reduce residual strains, and the residual strains, if any, will act to compress toward each other in lengthwise directions to improve the mechanical properties and attributes of that portion, with consequent less chance of its deformation and damage.
Moreover, the press-fitting portion of the press-in contact according to the invention is formed clearly in symmetry without any irregularity in shape and size, thereby preventing the ends of side walls of the U-shaped or V-shaped groove of the portion from separating from the inside of the through-hole of a printed circuit board, and the press-in contact from rotating in either direction in the through-hole, and hence preventing the contacting state with the board from becoming unstable and the holding force therebetween from decreasing.
The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.